1. Field of the Invention
The present invention relates generally to dental tools and equipment and more particularly to an apparatus for mixing, mulling and dispensing dental amalgam while preventing contamination of dental amalgam caused by contact with skin and while eliminating hazard of mercury poisoning.
2. Background of the Prior Art
In restoration of a tooth cavity, the dentist prepares cavity by drilling away decayed and soft portions of tooth in area of cavity. Then, a small portion of dental silver amalgam is prepared by mixing mercury with another metal, referred to here as "alloy", such as silver, copper, tin and zinc. Preparation of amalgam is commonly performed by a dental assistant while dentist is preparing cavity. Ratio of mercury to alloy portions mixed may be either excess mercury to alloy in the order of 7:5 or 8:5, or minimal mercury to alloy ratio of 1:1 or less. If excess mercury to alloy ratio is used, excess mercury must be expressed prior to condensing amalgam into cavity. Mercury expressing process is discussed in applicant's copending application entitled "Apparatus for Preventing Mercury Contamination." If minimal mercury to alloy ratio is used, amalgam is ready for application without the extra step of expressing excess mercury.
When amalgam is mixed such that each particle of alloy is coated with mercury and when excess mercury, if any, has been expressed, amalgam is loaded into a carrier. Tip of loaded carrier is then placed adjacent to prepared cavity and amalgam is forced from carrier and condensed into cavity with appropriate instruments.
Prior art teaches numerous devices and techniques designed to facilitate and improve effectiveness of this process. Many of these devices are directed toward facilitating removal of excess mercury when excess mercury to alloy ratio amalgam is used. Such devices are discussed in applicant's copending application entitled "Apparatus for Preventing Mercury Contamination" and that discussion is incorporated herein by reference.
As mentioned supra, necessity for removal of excess mercury may be avoided by use of minimal mercury to alloy ratio. This involves careful weighing of mercury and alloy portions to be mixed. Other methods of achieving minimal mercury to alloy ratio are use of factory preloaded and premeasured cartridges as taught by U.S. Pat. No. 3,612,352 to Smith, and devices that automatically measure portions of mercury and alloy as taught by U.S. Pat. No. 3,280,459 to Walker.
Devices directed to facilitating mixing of mercury and alloy are taught by U.S. Pat. Nos. 3,222,037 and 3,368,592 to Thiel, et al; 3,023,889 to Barr, and 3,828,434 to Mosch (trituration of mercury and alloy by way of mechanical vibration); U.S. Pat. No. 2,810,959 to Yates (paddle-shaped mixing tool for mixing amalgam in mortar); Walker, supra, and U.S. Pat. No. 3,611,573 (mixing amalgam in dispenser itself by mechanical mixing means disposed within dispenser).
Loading of prepared amalgam into dispenser has been facilitated by devices taught by both Thiel patents, supra, and U.S. Pat. No. 3,221,409 to Thiel, et al. (trituration process vibrates mixed amalgam from capsule into tube to be attached to dispenser); Mosch, supra, (tube itself is vibrated; tube then attached to dispenser); U.S. Pat. Nos. 1,188,417 to Dalbey, 3,521,356 to Newman, and 3,581,399 to Dragan (capsules or cartridges containing mixed amalgam loaded into dispenser); Smith, supra (mechanically shaping amalgam pellet for easy loading into dispenser). Loading of mixed amalgam into dispenser is avoided completely in Walker and Crawford, supra, in which mercury and alloy are mixed in dispenser itself.
Devices for facilitation of dispensing of amalgam are taught by U.S. Pat. No. 3,091,860 to Baughan (lever-action dispenser); U.S. Pat. No. 3,221,409 to Thiel, et al (ratchet-lever dispenser); U.S. Pat. No. 3,537,617 to Mendola (a second plunger slices off end of pellet forced into tube by a first plunger); Newman, supra, and U.S. Pat. No. 3,088,207 to Borsuk (pellet or plunger forced by compressed air); and Walker, supra (solenoid action).
Use of capsules, cartridges, and mixing in dispensers reduces opportunity of contamination of amalgam by way of contact with skin. This better assures a good filling of the cavity.
The prior art, however, has left two problems associated with the nature of amalgam and its constituents relatively unaffected. First, amalgam does not retain the form of a compact pellet or the like after mixing; instead, it tends to fall apart into many smaller particles and must be continually compacted or mulled during filling operation. This problem can severely impede the processes of loading a carrier, dispensing amalgam from carrier, and/or condensing amalgam into a prepared cavity. U.S. Pat. No. 2,716,816 to Braum teaches a device for mulling dental amalgam whereby contact between amalgam and skin is reduced. An advancement on mulling devices is taught in applicant's copending application entitled "Apparatus for Preventing Mercury Contamination". U.S. Pat. No. 3,222,037 to Thiel, et al., attempts to solve amalgam scattering problem by entrapping particles of amalgam in a dispenser tube. Even after entrapment in dispenser tube, amalgam is not mulled but remains in its separate and loose form.
Second, and probably most importantly mercury has been found to be a highly poisonous material. Poisoning can occur either through skin contact with liquid mercury or by breathing mercury vapor. A large number of articles have dealt with the ever-present danger of mercury contamination of dental operatories. See, e.g., Mantyla, Protection of Dental Personnel Through Proper Mercury Hygiene, DENTAL SURVEY (June 1973 58; Cedar, Mercury Vapor: A Hazard in the Dentist's Office, DENTAL STUDENT (February 1973) 28; Buchwald, Using Mercury Safely, DENTAL HYGIENE (July-August 1973) 231; Buchwald, More About Mercury Hygiene, Nixon and Rowbotham, Mercury Hazards Associated With High Speed Mechanical Amalgamators, BRITISH DENTAL JOURNAL (Oct. 5, 1971) 308; Borkowski and Mazza, Mercury Contamination of the Dental Office and Central Air Conditioning, NORTH CAROLINA DENTAL JOURNAL (Spring 1975) 13; Chandler, Rupp and Paffenbarger, Poor Mercury Hygiene From Ultrasonic Amalgam Condensation, 82 J.A.D.A. 553.
The present invention effectively eliminates any hazard of mercury contamination during the tooth restoration operation while permitting continual mulling of amalgam during actual filling operation. Furthermore, the present invention avoids step of removing excess mercury by factory preloading minimal mercury to alloy portions in syringe itself; avoids step of loading dispenser by providing for mixing of amalgam in dispenser itself; and facilitates dispensing by providing a dispenser of small size with simple, single-plunger dispensing action. Although present invention far surpasses capabilities of any device taught by prior art, it is less complex and less costly than many of the prior art devices.